Spectrometric instruments generally function to provide a spectral analysis of radiation pertaining to a sample or an astronomical source. The radiation source and/or the sample may be internal or external to the instrument. The instrument includes a wavelength analyzer, which comprises a spectral dispersion element such as a prism or, more commonly in precision instruments, an optical grating. The analyzer further includes a detector system. In one type, the detector has a single photosensitive component with a narrow entrance slit, and the dispersion element is mechanically rotated to scan a range of radiation wavelengths over the detector. In another type, the detector has an array of photosensitive pixel areas for detecting spectral increments across the range simultaneously. Array detectors have been made practical in solid state devices providing small adjacent pixels. The array may be either linear to receive a spectrum from a single dispersion element, or two dimensional for crossed dispersion elements. A two dimensional detector is disclosed in U.S. Pat. No. 4,820,048 (Barnard).
Modern precision spectrometric instruments include computer programming for calibration and treatment of the spectral information. U.S. Pat. No. 5,229,838 (Ganz et al) illustrates a grating with an array detector and teaches a system for calibrating amplitude linearity, and also teaches a particular type of instrument in which optical fibers are utilized to convey source radiation to a remote sample of liquid and back to the analyzer. U.S. patent application Ser. No. 834,448 filed Feb. 12, 1992 now Pat. No. 5,303,165, (Tracy et al), of the present assignee, discloses instrument standardization using computer programming, and also illustrates correction for background which generally represents radiation and instrument noise without the source in place. U.S. Pat. No. 5,023,804 (Hoult) teaches a method and apparatus for comparing spectra by means of computer programming.
With improvements in sensitivity resulting from advancing technology such as in the foregoing patents, it has been found that stray radiation is a limiting factor. Stray radiation results from imperfect gratings and internal reflections.
Therefore, objects of the invention are to provide a novel method and a novel apparatus to determine and correct for stray radiation in a spectrometric instrument. A further object is to provide improved spectral data that is corrected for stray radiation.